Apparatus for zone heating



United States Patent Office 3,211,881 Patented Oct. 12, 1965 3,211,881 APPARATUS FOR ZONE HEATING Eugene Jablonski, Baltimore, and John A. Redmond, Ellicott City, Md., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 28, 1962, Ser. No. 219,957 8 Claims. (Cl. 219-10.67)

This invention relates to zone heating apparatus and more particularly to such apparatus as is useful to effect crucible-free progressive zone melting of a rod-shaped or elongated material for purposes such as purifying, doping, or converting the structure of such material from polycrystalline to monocrystalline.

Apparatus of this type essentially employs an evacuable enclosure, an indicutive heating coil, a holder for the rod-shaped workpiece, and means for effecting relative longitudinal and rotary movements between the heating coil and the workpiece holder to obtain progressive zone heating of the workpiece along its length while being rotated within the coil.

It has been the practice heretofore to employ dynamic sliding seals cooperable between the evacuable enclosure and members extending from without into the interior of the enclosure for purposes of effecting the aforementioned relative longitudinal and rotary movements. Due to the reliance upon such dynamic seals, the degree of vacuum as well at its stability is influenced adversely according to the degree to which atmosphere leaks past these seals into the enclosure, which seals are vulnerable to destructive action of deposits of the heated material or workpiece which find their way to the moving parts of the seal and have an abrasive or deteriorating effect thereon.

Accordingly, it is a prime object of the present invention to provide a zone heating apparatus which overcomes the above objection with respect to use of dynamic seals while providing for effecting the relative longitudinal and rotary movements between the heating coil and the workpiece holder by motor means external .to the evacuable enclosure.

According to general features of the invention, the above object is realized by the embodiment of magnetic couplings between actuating members exterior to the enclosure and actuated members interior of the enclosure, 'in a manner which eliminates need for dynamic sealing.

Prior art zone heating apparatuses are also characterized either by employment of a movable heating coil within an evacuable water cooled housing external to the coil or by a fixed heating coil encircling a watercooled quartz cylinder'which defines the periphery of .the evacuable enclosure within which the workpiece is moved longitudinally and rotary wise relative to the coil. The former movable coil arrangements may require, for example, the use of sliding electrical contacts and/or flexible leads within the evacuable enclosure, which encourages arcing due to the increased voltage needed to compensate for power losses within such contacts and leads,

as well as requires an extensive cooling arrangement for the enclosure and/ or other complex arrangments, while the latter fixed-coil quartz-cylinder arrangement is subject to the problem of coupling the external heating coil 'to the workpiece rod within the cylinder, robbing heat from the workpiece by the quartz cylinder which must be water cooled, as well as the problem of effecting such water cooling in a manner which assures uniformity and prevents crack-inducing hot spots, and other problems such as clouding of the interior of the quartz cylinder by deposits from the rod materials and consequent obscuring of the view of the workpiece for control' purposes.

Accordingly, it is a further object of the invention to overcome these problems, and this is obtained by employment of a large metal evacuable enclosure with a fixed heating coil therein having a water-cooled shield adjacent to the heating coil.

Other objects and advantages of the invention will become apparent from the following detailed description of the invention taken in connection with the accompanying drawing in which:

FIG. I is a vertical front elevation view, partly in outline an partly in section, showing an illustrative embodiment of the invention; and

FIG. II is a view, partly in outline and partly in section, taken along the axis of a magnetic rotary coupling assemblage typical of several which are employed in the apparatus of FIG. I.

Referring now to FIG. I, the illustrative zone heating apparatus of the present invention comprises an evacuable enclosure 1, preferably of rectangular cross-section and with walls of stainless steel, which rests in an upright position adjacent to an operators control panel 2 on a hollow floor base 3 which affords the enclosure 1 and the control panel 2 a vertical position of convenient accessability to the operator. A pressure-tight-sealable door (not shown) with an observation window aligned with the heating zone is provided hingedly mounted on the housing 1 for opening the front of the housing preferably its full vertical height.

Secured to the housing 1 and extending vertically therein between top and bottom walls 4 and 5 and adjacent to the rear wall of such housing are horizontally-spacedapart vertical guide rods 6 and 7 of stainless steel, which serve to guide vertical movement of a workpiece-supporting frame which includes vertically-separated horizontal cross members 9 and 10 which are joined for vertical movement in unison by an elongated sleeve 11 slidable vertically on the guide rod 7. Guide collars 12 and 13 on cross members 9 and 10, respectively, slidably cooperate with the guide rod 6 to assure the maintaining of the proper horizontal alignment of such cross members in all vertical positions of the frame 8, to assure that the rod-shaped workpiece 14, which finds support from sleeves 15 and 16 on cross members 9 and 10, respectively, will be maintained in coaxial alignment with a fixed-position induction heating coil 17 mounted on the housing and insulated therefrom in a suitable manner (not shown).

For actuating the workpiece rod 14 in a vertical direction coaxially within and relative to the fixed heating coil 17, in accord with a feature of the invention, by a motor means 20 at the exterior of the evacuable enclosure 1 without the use of dynamic seals, the enclosure 1 is provided with a closed-bottom tubular portion 21 extending downwardly from the major rectangular boxshaped portion of the enclosure which defines an evacuable work chamber 22. Tubular portion 21 is open at its upper end through the bottom wall 5 to the work chamber 22 and serves to accommodate: a tubular frame-support rod 23 connected at its upper end to the workpiece-supporting frame 8; a push rod 24 having an upper portion extending upwardly into rod 23 in screw-threaded engagement with the interior of rod 23 at its lower end, and such push rod 24 having a lower portion of square cross section; a torque-output magnet member 26 coupled to the square portion of the push rod 24 for turning same; and thrust bearing means 27 via which the rod 24 and its vertical load is transferred to the bottom of tubular portion 21 of the enclosure. Rotation of the torque-output magnet member 26 for turning the push rod 24 to raise and lower the frame 8 via rod 23 and thereby move the workpiece 14 vertically through the heating coil 17, is effected by a torque-input magnet member 28 (FIGS.

1 and 2), which is rotated around the periphery of enclosure portion 21 by motor means 20 and a variablespeed transmission system including belt and pulleys 29, a gear mechanism 30, and another series of belts and pulleys 31.

' Each of the torque input and output magnet members 26 and 28 is ring-shaped and is polarized radially at a plurality of circumferentially spaced apart locations, as indicated in FIG. II. The poles of the inner member 26 are reversed from corresponding poles of the outer member 28 so that they magnetically lock rotarywise one with the other and serve as a torque coupling between the interior and exterior of enclosure portion 21 which separates them radially and is of a material, such as stainless steel, which does not interfere with the magnetic flux coupling between torque members. No dynamic fluid pressure sealing means is required in this arrangement, as per an object of the invention as previously set forth.

Such dynamic-seal-free torque coupling is employed also for effecting rotation of the workpiece 14 via a vertical workpiece support rod 35 of square cross section which carries at its upper end a bottom holder 36 for the workpiece 14, which holder is rotatably supported by the cross member of the frame 8. A respective closed-bottom cylindrical portion 21 of the enclosure 1 serves to accommodate extension of the rod 35 and disposition of a respective output torque magnet member 26 which is rotatably supported via respective thrust bearing means 27 by an annular collar fixed to such portion 21. By rotation of a respective outer input torque magnet member 28 by a variable speed motor and gear assemblage 37 via respective belt and pulley means 38, the rod 35 and the workpiece holder 36 are rotated irrespective of the vertical position which the frame 8 carries the bottom workpiece holder 36.

The dynamic-seal-free torque coupling is repeated also at the top of the evacuable enclosure 1 in similar manner to rotate a screw-threaded rod 42 which carries an upper workpiece holder 45 and cooperates with a screw-threaded portion 46 of frame cross member 9 to effect relative vertical movement between the upper and bottom workpiece holders 45 and 36 to effect the so-called-stretch or squeeze of the workpiece rod 14 during progression of the molten zone 50 therealong by operation of a reversible variable speed motor drive assemblage 49.

For accommodating evacuation of the enclosure 1, a flanged nipple 51 is provided the enclosure for connection to a vacuum system. Sight ports 52 and 53 at opposite sides of the heating coil 17 enable observance of the molten zone 50 of the workpiece by optically-responsive control means (not shown) for regulating such as stretch-squeeze and/or the supply of electrical energy to the induction heating coil 17. Heat resistant glass windows 54 cover the sight ports 52 and 53.

To protect components of the apparatus disposed within vacuum work chamber 22 as well as the walls of the enclosure 1 from excessive heat and from deposits of workpiece material, a water-cooled hollow cylindrical shield 55 of such as copper, encircles the heating coil 17 and its leads (not shown) extending inwardly from the rear wall of the enclosure. The shield 55 has aligned openings 56 at top and bottom to accommodate extension of the workpiece rod 14 therethrough, as well as side openings 57 to enable observance of the molten zone 50 of the workpiece via the sight ports 52 and 53 in enclosure 1.

To enable the upper end of the workpiece rod to be gripped without imposing any bending action thereon,

the upper workpiece holder 45 takes the form of a twofingered clamp pivotally connected at 59 to the rod 42 which grips the upper end of the workpiece at opposite points on its periphery along a narrow line of contact.

In operation of working models of the exemplified apparatus the heating coil 17 is energized by alternating current within the frequency range of 10 kc. to 4 mc., dependent on the resistivity and diameter of the bar being processed, the motor means 20 is operated to obtain a vertical movement of the frame 8 via rods 23 and 24 and magnetic rotary coupling members 26 and 28 at a rate which may be varied from a fraction of an inch per hour up to 430 inches per hour according to speed regulation of the driving means by control means (not shown), While the workpiece is rotated by the variable speed motor and gear assemblage 37 as a selected speed from several r.p.m. up to rpm. Stretch or squeeze may be effected as desired by operation of drive assemblage 49 to effect vertical movement of the upper Workpieceholder 45 relative to the lower workpiece holder 36 by rotation of the screw-threaded rod 42, at rates which may be varied from a fraction of an inch per minute up to six inches per minute, for example. Such working model also provides for a scanning stroke of eighteen inches, accommodates a workpiece up to twenty four inches long, and provides for a stretch or squeeze distance of two and one-half inches.

To prevent entry of the upper and lower workpiece holders 45 and 36 into the heating coil during their vertical movement, commercially-available magnetic limit switches 60 are provided which are mounted outside the enclosure 1 on its rear wall for magnetic actuation by magnet elements 61 and 62 carried by the upper holder 45 and cross member 10, respectively. The rear wall of the enclosure 1 is of a material such as stainless steel which does not interfere with the coupling of magnetic flux between elements 61 and 62 and their respective limit switches 60.

Although an exemplified embodiment of the invention has been shown schematically and described, it will be understood modifications may be made within the spirit and scope of the appended claims.

We claim as our invention:

1. Apparatus for crucible-free zone melting of rodshaped material, comprising a pressure-tight metal enclosure, a fixed induction heating coil disposed in said enclosure with its axis extending in a vertical direction, vertically spaced-apart holders within said enclosure for securing the rod material in extension along said axis through said heating coil, and means for actuating said holders in a vertical direction to obtain scanning of the rod-shaped material by said heating coil.

2. Apparatus for crucible-free zone melting of rodshaped material, comprising a pressure-tight enclosure, a fixed heating coil disposed in said enclosure with its axis extending in a vertical direction, vertically spacedapart holders Within said enclosure for securing the rod material in extension along said axis through said heating coil, motor means disposed outside said enclosure, screw-threaded means within said enclosure rotatable for effecting vertical movement of said holders to obtain scanning of the rod-shaped material by said heating coil,

and means transmitting rotary actuating force from the motor means to the screw-threaded means by transmission of magnetic flux through a wall of said enclosure.

3. Apparatus as set forth in claim 2, further characterized in that the last named means comprises inner and outer rotatable permanent magnet means disposed within and without, respectively a cylindrical wall portion of said enclosure.

4. Apparatus as set forth in claim 2, further comprising shielding means disposed within said enclosure around said heating coil.

5. Apparatus for crucible-free zone melting of rodshaped material, comprising a pressure-tight metal enclosure, a fixed induction heating coil disposed in said enclosure with its axis extending in a vertical direction, vertically spaced-apart holders within said enclosure for securing the rod material in extension along said axis through said heating coil, means for actuating said holders in a vertical direction to obtain scanning of the rod-shaped material by said heating coil, means for rotating the bottom one of said holders, and means for eifecting relative vertical movement between said holders.

6. Apparatus for crucible-free zone melting of rodshaped material, comprising a pressure-tight enclosure, a fixed induction heating coil disposed in said enclosure with its axis extending in a vertical direction, vertically spaced-apart holders within said enclosure for securing the rod material in extension along said axis through said heating coil, motor means disposed outside said enclosure, actuating means disposed within said enclosure for efiecting vertical movement of said holders, rotation of the bottom one of said holders, and relative vertical movement therebetween all exclusively by rotary input motion, and means dependent on rotary transmission of magnetic flux through pressure-retaining wall means of said enclosure for operatively connecting said motor means to said holders.

7. The apparatus as set forth in claim 6, wherein the last named means includes a plurality of rotatable magnet members arranged coaxially within and without hollow cylinder shaped wall means defining pressure-retentive portions of said enclosure.

8. In apparatus for crucible-free Zone melting of rodshaped material, comprising a pressure-tight enclosure and a vertically-moved rotatable holder for an end of such material, the combination therewith of a rotatable shat-t means disposed in said enclosure and operatively connected to said holder, a rotatable torque-output magnet means disposed in said enclosure at a fixed location therein, said torque-output magnet means being coupled to a longitudinal portion of said shaft in torque-transmissible relationship therewith for turning same and in axially-slidable relationship therewith to permit longitudinal advancement of said shaft relative thereto during vertical movement of said holder, and a fixed-verticalposition rotatable torque-input magnet means disposed outside said enclosure and coupled magnetically to said torque-output magnet means for turning same.

References Cited by the Examiner UNITED STATES PATENTS 2,366,562 1/45 Schug 3l0l04 2,870,309 l/59 Capita 219-10.43 2,893,847 7/59 Schweickert et al. 23273 2,970,548 2/61 Berner 3l0l04 3,009,973 11/61 Emeis 13-1 3,050,646 8/62 Eddy et al 310-104 3,052,805 9/62 Hudson 310104 3,074,785 1/ 63 Gremmelmaier 2327.3

FOREIGN PATENTS 971,644 9/64 Great Britain.

RICHARD M. WOOD, Primary Examiner.

Disclaimer 3,211,881.Eugene Jablonski, Baltimore, and J 07m A. Redmond, Ellicott City, Md. APPARATUS FOR ZONE HEATING. Patent dated Oct. 12, 1965. Disclaimer filed Nov. 15, 1965, by the assignee, W estz'nghouse Electric Corporation.

Hereby enters this disclaimer to claims 1 and 5 of said patent. [Ofiicz'a-l Gazette May 10, 1.966.] 

1. APPARATUS FOR CRUCIBLE-FREE ZONE MELTING OF RODSHAPED MATERIAL, COMPRISING A PRESSURE-TIGHT METAL ENCLOSURE, A FIXED INDUCTION HEATING COIL DISPOSED IN SAID ENCLOSURE WITH ITS AXIS EXTENDING IN A VERTICAL DIRECTION, VERTICALLY SPACED-APART HOLDERS WITHIN SAID ENCLOSURE FOR SECURING THE ROD MATERIAL IN EXTENSION ALONG SAID AXIS 